Membrane Protein Solid State NMR: PISEMA Development and the M2 Tetramer Structure

膜蛋白约占所有基因组的30%。今天，蛋白质数据库中只有不到40种独特的膜蛋白结构。膜蛋白为细胞执行许多关键功能，它们与水溶性蛋白在氨基酸组成、稳定结构的力量、内部动力学等方面有很大不同。出售状态核磁共振是实现在脂质双分子层环境三维高分辨率结构的演示技术。该技术独特地利用完全水合的脂质双分子层来溶剂化蛋白质样品。这项工作将进一步发展用于结构表征的主要固态核磁共振实验，PISEMA。包括在Lee-Goldburg序列中使用斜坡脉冲在内的一些修改表明，PISEMA实验的鲁棒性得到了显著提高。先进的核磁共振探针在高场磁体中具有平衡的射频电路，将有助于实现这一目标。对α螺旋蛋白的PISEMA光谱的分析已经成为《磁共振杂志》和《蛋白质科学》的封面故事。固态核磁共振数据的表征直接导致了脂质双分子层内螺旋的倾斜和旋转方向的描述。在这里，这个分析将使用数学表达式来展示如何解决结构解中的简并，通过显示预测α， 310和pi螺旋的独特光谱模式，并通过表征脂质双分子层平面上螺旋的更复杂的光谱模式。此外，本项目旨在解决脂质相变以上水合脂质双层中44 kDa四聚体M2质子通道的完整骨架结构和组装。在这个项目中，克罗斯博士和他的同事将开发一种独特的方法来确定膜蛋白在其天然环境中的三维结构-包围每个细胞的脂质膜。这些蛋白质控制着所有进入和离开细胞的东西，它们负责在细胞之间接受和发送信息。给定基因组中30%或更多的蛋白质是膜蛋白，但技术对其结构表征非常有限。克罗斯博士拥有一支由化学家、数学家和生物物理学家组成的独特团队，他汇集了核磁共振方法开发的必要技能，该方法现已被证明可以实现膜蛋白的独特结构。克罗斯博士和他的同事正在改进这项技术，并提高其灵敏度，以用于更广泛的应用。这项研究将在膜蛋白生物物理学和结构生物学领域产生广泛的影响，化学、生物和数学学科的学生将在一个成熟的跨学科环境中接受培训。

Membrane proteins represent approximately 30% of all genomes yet characterized. Today, less than 40 unique membrane protein structures are in the Protein Data Bank. Membrane proteins carry out numerous critical functions for cells and they are vastly different from their water-soluble counterparts through: their amino acid composition, the forces that stabilize their structure, their internal dynamics, etc. Sold state NMR is a demonstrated technology for achieving 3D high resolution structure in a lipid bilayer environment. This technology uniquely utilizes fully hydrated lipid bilayers for solvating protein samples. This work will further develop the primary solid state NMR experiment used for the structural characterization, PISEMA. Several modifications including the use of ramped pulses during the Lee-Goldburg sequence suggests significant gains in making PISEMA a more robust experiment. Advanced NMR probes with balanced RF circuits in high field magnets available at the NHMFL will be a great help in achieving this goal. The analysis of PISEMA spectra of alpha-helical proteins has led to cover stories in both the Journal of Magnetic Resonance and Protein Science. The characterization of solid state NMR data leads directly to a description of the tilt and rotational orientation of the helix within the lipid bilayer. Here, this analysis will be advanced using mathematical expressions to show how degeneracies in the structural solutions are resolved, by showing that unique spectral patterns are predicted for alpha, 310, and pi helices, and by characterizing the more complex spectral patterns for helices in the plane of the lipid bilayer. Moreover, it is the aim of this project to solve the complete backbone structure and assembly of the 44 kDa tetrameric M2 proton channel in hydrated lipid bilayers above the phase transition of the lipids. In this project Dr. Cross and his colleagues will develop a unique approach for determining the three dimensional structure of membrane proteins in their native environment - the lipid membrane that surrounds each cell. These proteins control everything that enters and leaves the cells, and they are responsible for accepting and sending information between cells. 30% or more of the proteins of a given genome are membrane proteins and yet technologies are very limited for their structural characterization. With a unique team of chemists, mathematicians and biophysicists, Dr. Cross brings together the necessary skills for the development of a Nuclear Magnetic Resonance methodology that has now been demonstrated to achieve unique structures of membrane proteins. Dr. Cross and his coworkers are refining the technology and enhancing its sensitivity for greater applications. This research will have a broad impact in both the fields of membrane protein biophysics and structural biology and students in chemical, biological and mathematical disciplines will be trained in a proven interdisciplinary environment.